This laboratory has studied the molecular basis of embryogenesis in Xenopus laevis and the zebrafish, with special emphasis on axis determination and pattern formation. These events are thought to be controlled by cell-to-cell signaling and by the spatially and temporally regulated action of transcription factors. The Xlim-1 gene encodes a LIM-homeodomain protein that has been shown to be involved in the functions of the Spemann organizer in neural induction and mesoderm patterning. This gene is also important in kidney formation. The function of Xlim-1 is being studied by application of an oligonucleotide antisense strategy. Modified antisense oligonucleotides that are stable in the embryo have proven valuable tools for the analysis of Xlim-1 function during gastrulation. A screen for developmentally regulated genes is being conducted in zebrafish. By screening for genes with restricted expression patterns, valuable information is collected about gene control of embryogenesis. One gene isolated in this approach, named iro3, has been shown to have a role in organizer function in the gastrula. A zinc finger transcription factor isolated from zebrafish named biklf has been shown to constitute one of the earliest markers for blood formation and to be involved in erythroid cell differentiation. In addition, a genetic screen has been initiated that uses a chemical mutagen expected to generate deletions in the zebrafish genome. Such lesions are expected to be very useful in the genetic and functional characterization of zebrafish genes.